Studies of the distributions of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) by the bis-(thioacetoxy) aurate (I) electron microscopic (EM) histochemical method will be extended to the ciliary ganglion, carotid body, and other appropriate tissues of the cat and other species. The current search for neurotrophic factors essential for the maintence of AChE at postsynaptic sites in the cat superior cervical ganglion will be continued by the in-vivo perfusion technique developed by G.A. Ruch. Investigation of the effects of preganglonic denervation and of treatment with selective inactivators of AChE an BuChE, alone and in combination, on the electrophoretically separable isoenzymes of AChE will be extended.